Cracking hydrocarbon residua

ABSTRACT

Hydrocarbon residua boiling mostly 1,000* F. and above are catalytically hydrocracked under liquid phase conditions and novel recycle ratios to obtain a product which is predominantly an aromatic gas oil which is eminently suitable either as a solvent or as feed to commercial hydrocracking operations. Although the upper boiling limit of this gas oil may be in the range of 600*-800* F., the process is illustrated with separation into fractions boiling 650* F.- and 650* F.+. An amount of the low-boiling and high-boiling fractions are recycled so that the feed mixture to the reaction zone contains 20 percent of the lowboiling fraction, 40 percent of the high-boiling fraction, and 40 percent of fresh feed while the high-boiling fraction is recycled to extinction at a rate such that the amount present in the feed mixture to the reactor is equal to the amount in the product. 125 percent of an acyclic hydrocarbon modifier is added to the reaction mixture to act as a free radical acceptor under such conditions that is has a residence time of 1 hour or less as compared to 1 to 6 hours for the residua-recycle mixture.

United States Patent [72] Inventors Ralph B. Mason ABSTRACT: Hydrocarbonresidua boiling mostly 1,000 F. Denham Springs; and above arecatalytically hydrocracked under liquid phase l Baton 98 boul conditionsand novel recycle ratios to obtain a product which [21] Am. N 840,935 ispredominantly an aromatic gas oil which is eminently suita- [22] FiledJuly 1 ble either as a solvent or as feed to commercial hydrocrackingPatented 1 1971 operations. Although the upper boiling limit of this gasoil may [73] Assignee E850 R searc an Eng n ring mp y be in the range of600-800 F the process is illustrated with separation into fractionsboiling 650 F. and 650 F.+. An amount of the low-boiling andhigh-boiling fractions are recy- [54] CRACKING HYDROCARBON RESIDUA cledso that the feed mixture to the reaction zone contains 10 Claims 1Drawing percent of the low-boiling fraction, percent of the high- [52]11.8. (I 208/112 boiling fraction, and 40 percent of fresh feed whilethe high- [51] lm. Cl. Clog 13/02 iling fra i n i recycled to extinctionat a rate such that the Field of Search 208/112, amount present in thefeed mixture to the reactor is equal to 123, 145 the amount in theproduct. 1-25 percent of an acyclic hydrocarbon modifier is added to thereaction mixture to act (defences Cited as a free radical acceptor undersuch conditions that is has a FOREIGN PATENTS residence time of 1 houror less as compared to l to 6 hours 1,007,327 10/1965 Great Britain208/111 f F Primary Examiner-Delbert E. Gantz Assistant ExaminerG. E.Schmitkons Attorneys-Pearlman and Stahl and C. D. Stores 43o s5oF l8l'ims PRODUCTS RECYCLE GAS a /3 (H AND GASEOUS g MODIFIER) r 9 g 8 aCONDENSER AND GAS SEPARATOR FLASH CHAMBER LIQUID PHASE DRAW OFFHYDROCRACKER 5 2 RECYCLE D R REs|nuE I4 \I 6 I5 20 ssom CRACKINGHYDROCARBON RESIDUA BACKGROUND OF THE INVENTION This invention relatesto the catalytic conversion of hydrocarbon residua and more particularlyrelates to the hydrocracking of heavy residua under conditions ofextinction recycle.

It is expected that steam cracking facilities will expand in the future,particularly in Europe. This will require means for easily disposing ofthe considerable amounts of tar which are a concomitant part of thesteam cracking process. One obvious method is to upgrade these tars aswell as other residues by thermally treating the tars with a hydrogendonor diluent material. The donor diluent is a hydrogen-containingmaterial, aromatic-naphthenic in nature, that has the ability to take uphydrogen in a hydrogenation zone and readily release it to ahydrogen-deficient oil in a thennal cracking zone. Unfortunately,however, there is often undesired coke deposition at hot spots andpreheater zones, leading to plugging of the equipment.

In Ser. No. 839,220 filed July 7, 1969 (now abandoned) for the presentapplicants it was shown that residual materials could behydrodepolymerized in a liquid-phase operation in which that portion ofthe product boiling above 650 F. is recycled to extinction and theamount of material (including recycle) in the feed boiling below 650 F.is maintained between 20 and 50 percent of the total composition fed tothe reaction zone in which the amount of 650 F. recycle and the amountof 650 F. in the product are kept at about the same level and yields of95 volume-percent gas oil obtained particularly in the additionalpresence of an acyclic hydrocar bon acting as a free radical acceptor.

SUMMARY OF THE INVENTION ln accordance with the present invention it hasbeen found that results equally as good or better than those obtained inSer. No. 839,220 (supra) can be obtained by subjecting residualmaterials to catalytic hydrocracking in the liquid phase in operation inwhich the 650 F. material is recycled to extinction and the amount of650 F. material and the amount of 650 F. material and the amount offresh feed fed to the reactor zone is maintained in a ratio ofapproximately 40:20:40 weight-percent and the amount of 650 F. materialrecycled to extinction and the amount of 650 F. in the product are keptat about the same level, i.e. leveling ofi at about 40 percent. Wheredesired the recycle stream may be further processed in a cokingoperation to produce coke or binder oil. Yields of 95 volume-percent of650 F. can easily be obtained. The presence of the 650 F. materialprovides solvency which permits mobility and moderate temperatures andthus minimizes coke make.

It is also a feature of this invention that acyclic hydrocarbons bothstraight-chain and branched and both saturated and unsaturated whenpresent in amounts of 1-25 percent,

preferably l percent, acting as free radical acceptors increase productyields. To achieve maximum byproduct utilization from, the added acyclicfree-radical acceptors, it is preferred that the residence time of theacceptor be maintained relatively short, i.e. 1 hour or less.

BRIEF DESCRIPTION OF THE DRAWING The drawing represents in diagrammaticform a preferred method for carrying out the process of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, ahydrocarbon residue, having a Conradson carbon number between and 40 anda substantial amount boiling at 1,000 F. and above such as thermal tarfrom steam cracking, reduced crude, shale oil residue, liquified coalfractions, and the like is slurried with 0.5 to 5 weight-percent acatalyst such as Harshaw nickel and is fed by line 1 and mixed withlower-boiling material, such as gas oil,

preferably recycled from a later stage of the process which entersthrough line 2, mixed with 500-5 ,000 SCF of hydrogen or a nonoxidizinggas per barrel of feed introduced by line 3. Gas oil or the like acts asa solvent for the tar and pennits easy pumping at moderate temperaturesand prevents coking at hot spots in the system. The mixture is passed byline 4 into the bottom of hydrocracker 5 where the mixture is maintainedat a temperature of 700900 F., (preferably 750-775 F.) and undersufficient pressure to maintain it in the liquid phase, e.g. 50-1000p.s.i.g. A free-radical acceptor or modifier,

preferably an acyclic hydrocarbon, which may be a parafiin oriso-parafim of four to 20 carbon atoms per molecule, or an olefin oriso-olefin of two to 20 carbon atoms per molecule or mixtures thereof isadded by lines 6 and 7. Suitable hydrocarbons include n-heptane;n-pentane; 2,2,4-trimethyl pentane; 2,2,4-trimethyl pentane-l;2,4,4-trimethyl pentane-2, low-octane unsaturated naptha fractions, anormal C -C virgin naphtha, catalytic heavy naphtha, heavy alkylates, al00- l 65 F. hydroformate fraction, the 2l0-400 F. fraction may be madeby polymerizing propylenes and butylenes with l-I PO on kieselguhr, andthe like. These hydrocarbons are added in amounts of about 1 to 25percent based on tar feed and are sprayed, jetted of otherwise passedthrough the liquid tar phase in hydrocracker 5, into the vapor phase andremoved overhead through line 8. The residence time of the modifieradded through line 7 should range from about 5 minutes to l hour. Thepresence of the hydrocarbon modifiers at such short residence timesresults in reduced coke and gas loss. However some of the modifier isconsumed in the process. When n-heptane is the modifier the degradationproducts are predominately normal hydrocarbons, namely, n-butanen-pentane, n-hexane, etc. whereas when iso-octane is used thedegradation products are predominately branched, i.e., isobu tane,isopentane and branched C and C, paraffins. The use of2,2,4-trimethylpentane and olefins of a similar skeletal structureresults in the production of the importing blending agent, triptane.Without intending to limit the invention to any theory of what occurs,it is believed that the mechanism is one in which the modifier is beingconsumed with accompanying hydrogen exchange, demethanation, alkylation,isomerization, aromatic disproportionation and probably every knownhydrocarbon reaction. The most plausible explanation is a free radicalmechanism in which the condensed ring aromatic components of the tardepolymerize with the formation of free radicals which attach themselvesto the modifier as a sink. In doing so the modifier in turn forms freeradicals involving stepwise degradation and rearrangement reactionsleading to gaseous products, coke, etc.

From the above it appears that conditions of short residence times forthe modifier (less than 1 hour) coupled with fairly long residence timesfor the tar feed (1 to 6 hours) is important for best results.

The modifier leaving hydrocracker 5 through line 8 is passed toseparator 9 from which hydrogen and uncondensed gas is recycled by line10. Condensate from separator 9 is passed by line 11 to fractionator 12from which low-boiling products are removed by line 13 and unreactedmodifier and entrained higher-boiling components by line 14. Thisunreacted modifier is recycled to depolymerizer 5 by lines 15 and 7.

. Liquid products are withdrawn from hydrocracker 5 by line 16 andpassed through filter 22 where catalyst, coke and/or other solidcontaminants are removed and then passed and recycled to hydrocracker 5by line 23. If desired the solids from filter 22 may be passed to aburner where carbonaceous material is removed and thence a hydrocarbonreduction zone to provide a reduced metal and/or sulfide suitable forrecycling to the hydrocracker as catalyst therein. Liquid products arepassed to flash chamber 17 where they are separated into productsboiling above and below 650 F. Those boiling below 650 F. are eitherdrawn off as make products through lines 18 and 21 or are recycled tohydrocracker 5 by line 18, 2 and 4. Products boiling above 650 F. arerecycled by lines 20, 15, and 7.

The amount of products boiling below and above 650 F. recycled iscritical, and must be in the ratio of 40 percent 650 F. :20 percent 650'F. :40 percent fresh feed. This control is made possible by withdrawingan amount of 650 F. material from the system by line 21 necessary tomaintain the proper recycle ratio. The product drawn off through line 21is suitable as such, as solvent for use in the chemical industry or maybe further fractionated to separate out desired solvent and aromaticfractions and if desired with recycle of the highboiling material.

The recycle of the 650 F. material on the otherhand is also controlledso that the amount of this material fed to the hydrocracker based ontotal feed will be substantially the same as the amount of 650 F.material found in the product, based on tar blend. Generally this isbetween 35 and 45 percent preferably 39-41 percent. While it is notlimited to be bound by any theory as to mechanism involved, it isbelieved that the beneficial results obtained are due to an equilibriumphenomenon in which an equilibrium exists between the condensed ringaromatic-containing 650 F. fraction and the lower-boiling 650 F.hydrocracked fraction. Excessive amounts of the 650 F. fraction willretard the hydrocracking, limit throughput of the depolymerization feedand incur excessive handling costs.

The following examples are included to illustrate the effectiveness ofthe instant process for the depolymerization of tars without, however,limiting the same.

EXAMPLE 1 A steam-cracked tar consisting of 35.7 percent materialboiling 430-650 F 34.3 percent boiling 6501000 F., and

' 30 percent boiling 1000 F. was subjected to several cycles ofhydrodepolymerization for 4 hours each at 775 F. under 1000 p.s.i.g.hydrogen pressure while about percent n-heptane, based on tar wasthoroughly agitated with the liquid. The following data were obtained:

Run No. 68 70 72 Grams of Catalyst 20.8 20.4 20.0 Tar Feed, Grams 424.9376.5 464.6 Wt. b Tar 39.7 37.3 38.5 Wt. i 650 F.-- Recycle 19.1 19.420.5 Wt. 650' F.+ Recycle 41.2 43.3 41.0 n-Heptane Employed,

' Grains 51.0 50.0 50.0 Operating conditions Avg. Temperature, F. 775775 775 775 Hours of Run 4 4 2' 2 Pressure, p.s.i.g.

A! Star! L000 1,000 1,000 1.000 Maximum 1,500 1,520 1,200 1,000Recoveries, Grams n-Heptane 34.8 29.2 32.5 Total Solids 18.8 21.6 19.7

Iv Carbon 14.64 29.5 k Hydrogen 0.92 [.42 I: Nickel 58.] 55.0 Liquid 6:Gas ex. n-

Heptane C -Gas 20.0 24 19.5 C,221 F. Cut, Grams 3.2 2.6 2.3 221-375 F.Cut, Grams 9.8 9.2 9.2 375-430" F. Cut. Grams l2.8 14.1 l9.0

430-650 F. Cut, Grams 214.4 170.9 239.0

650 F.+ Portion 175.9 162.3 188.5

Coke 2.9 6.7

Coke Gas, Wt.

Based on Fresh Tar 1.3 1.3 1.3 Est. Vol. 650 F. on

Recycle to Extinction 104 I04 104 After 2 hours at 775.F. temperaturewas cooled to 600 F. and pressure was reduced to 200 p.s.i.g. by ventingthrough cooled traps. Pressure was brought to 1,000 p.s.i.g. withhydrogen addition and temperature was brought to 775 F. for 2 additionalhours. Hydrogen additions were made during both periods on heat tocompensate for hydrogen uptake.

The above data show that recycle of the 650 F. material to extinctioncan be obtained with only minor losses to coke and gas when employing acatalytic system and in which the ratio of fresh feedz650 F. recyclez650F. recycle is maintained at 40:20:40, approximately.

The nature of the present invention having thus been fully set forth andspecific examples of the same given what is claimed as new, useful andunobvious and desired to be secured by Letters Patent is:

l. A process for the catalytic hydrocracking of hydrocarbon residuahaving Conradson carbon numbers between 5 and 40 which comprises heatingsaid residua in the presence of hydrogen and a particulatehydrogenenation catalyst under a pressure sufficient to maintain theresidua in the liquid phase and at a temperature between 700 and 900 F.in the additional presence of l to 25 percent of an acyclic hydrocarbonmodifier, having two to 20 carbon atoms, removing reacted residua andseparating it into a low-boling fraction boiling below 650 F. and ahigh-boiling fraction boiling above 650 F. and recycling an amount oflow-boiling fraction such that the ratio of fresh feed to high-boilingrecycle to low-boiling recycle is maintained at about 40:20:40 percent.

2. The process of claim 1 in which the residence time of the acyclichydrocarbon modifier is 1 hour or less and that of the residua-recyclemixture is 1 to 6 hours and the catalyst is pulverized Harshaw nickel.

3. The process of claim 2 in which the modifier is n-heptane.

4. The process of claim 2 in which the modifier is n-pentane.

5. The process of claim 2 in which the modifier is 2,2,4- trimethylpentane.

6. The process of claim 2 in which the modifier is 2,2,4- trimethylpentanel 7. The process of claim 2 in which the modifier is 2,4,4-trimethyl pentane-2.

8. The process of claim 2 in which the modifier is a normal C -C virginnaphtha.

9. The process of claim 2 in which the modifier is a l00-l 6 5 F.hydroformate.

10. The process of claim 2 in which the modifier is the 2l0-400 F.fraction made by polymerizing propylenes and butylenes with H PO onkieselguhr.

l l l

2. The process of claim 1 in which the residence time of the acyclichydrocarbon modifier is 1 hour or less and that of the residua-recyclemixture is 1 to 6 hours and the catalyst is pulverized Harshaw nickel.3. The process of claim 2 in which the modifier is n-heptane.
 4. Theprocess of claim 2 in which the modifier is n-pentane.
 5. The process ofclaim 2 in which the modifier is 2,2,4-trimethyl pentane.
 6. The processof claim 2 in which the modifier is 2,2,4-trimethyl pentane-1.
 7. Theprocess of claim 2 in which the modifier is 2,4,4-trimethyl pentane-2.8. The process of claim 2 in which the modifier is a normal C5-C7 virginnaphtha.
 9. The process of claim 2 in which the modifier is a 100*-165*F. hydroformate.
 10. The process of claim 2 in which the modifier is the210*-400* F. fraction made by polymerizing propylenes and butylenes withH3PO4 on kieselguhr.